Effect Of Cr On The Microstructure And Mechanical Properties Of Fe-28Mn-11Al-1.6C Steel

Low density and high strength steel has good comprehensive properties such as low density,corrosion resistance,high strength and toughness.This kind of steel has great application potential in automobile,military industry,construction and other fields.Among different types of low density steel,Fe-Mn-Al-C series low density steel is favored by researchers because of its higher specific strength and good ductility.However,it exists in high-Al Fe-Mn-Al-C low-density steelκ-the precipitation of carbide is difficult to control,while Cr can control the precipitation ofκ-carbide.In this paper,low-density high-strength steel with composition of Fe-28Mn-11Al-1.6C-x Cr（x=0,3,5）has been developed.The thermal deformation behavior of the experimental steel has been studied by optical microscopy（OM）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray diffraction（XRD）κ-the effect of carbide precipitation behavior and Cr on the microstructure and properties of experimental steel before and after quenching.The recrystallization degree of Fe-28Mn-11Al-1.6C-x Cr（x=0,3,5）austenitic low density experimental steel increases with the increase of deformation temperature and strain rate.The optimum range of hot working process is:0Cr steel:920-980℃,0.01-0.05 s^-1 and 1030-1050℃,0.01-0.03 s^-1;3Cr steel:990-1050℃,0.01-0.08 s^-1 and 1030-1050℃,0.9-10 s^-1;5Cr steel:1000-1050℃,0.01-0.87 s^-1.After solution treatment,the as-cast experimental steel,κ-carbides can age naturally at normal temperature.After aging at room temperature,the microstructure of rolled experimental steel is composed of austenite andκ-carbide composition,with the increase of Cr content,κ-the mass fraction of carbide precipitation decreases.Cr affectedκ-precipitation position,particle size and quantity of carbide.In Cr-containing steelκ-carbides are concentrated in the high dislocation density region;In 0Cr steelκ-carbide size is 60-200 nm,in 3Cr and 5Cr steelκ-the carbide size is 20-40 nm and 5-27 nm respectively.The elongation of 0Cr steel and 3Cr steel increased from brittle fracture and 22% to 23% and 38%respectively after the solution and water cooling at 1000℃.The elongation of 5Cr steel decreased from 26%to 20%due to the presence of Cr-containing carbides.After solution water cooling at 1050℃and above,the three kinds of experimental steels are brittle fracture under room temperature tension.In practical application,solution water quenching should be avoided in these temperature ranges.